VMWare ESXi: backup of data on vm with raw mappings to usb disk attached to server?

I have this HP NL 40-server. On it a vm (Windows 2012 R2) with 3 SATA disks in RAID.
Now I'd like to backup the data on this RAID-volume. Which is the most effective way to do this? There are 4 slots in the server, so I could add a 4th SATA disk to backup to but I'd prefer to extend my raid to it.

I have the option to add an usb controller to the vm. The idea is to attach an external usb drive to the hp nl40 and make backups to it.

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*add a 4th disk to my physical server, use raw mapping and backup to that => in this case I'm afraid I might messup the raw data when I plugin the disk into another server => don't prefer this option

*add a 4th disk to my physical server as datastore and add a vmdk which I attach to the backupserver => might have performance loss(?) but when I plugin the disk into another esxi, I can mount it and recover?

*add a 4th disk to my physical server, use raw mapping and backup to that => in this case I'm afraid I might messup the raw data when I plugin the disk into another server => don't prefer this option

Even a Windows Backup to 4th disk will be great and fast!

*add a 4th disk to my physical server as datastore and add a vmdk which I attach to the backupserver => might have performance loss(?) but when I plugin the disk into another esxi, I can mount it and recover?

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